The invention relates to a projector.
In order to expand or constrict the light field of a projector having a projector housing in which a lamp and a paraboloidal reflector are arranged, and whose light exit opening is covered by one or more protective plates, the lamp is displaced in an axial direction relative to the reflector such that in order to set the shape of the light field the lamp is moved either into the reflector or in the direction of the focal point of the reflector, in order to obtain a bundling of the light field, or is moved out of the reflector away from the focal point of the reflector, in order to achieve an expansion of the light field. A maximum bundling of the light is obtained when the lamp is located exactly at the focal point of the paraboloidal reflector such that the exiting light beams exit the projector in a fashion substantially parallel to one another. In the case of a wide light field, the lamp is stationed in a forward position in the reflector, and the exiting light beams behave convergently, that is to say at first they are condensed and cross one another in a region in front of the light exit opening of the projector and then diverge. The distribution of the exiting light beams is frequently characterized in this case via the half scattering angle.
A large half scattering angle signifies a wide light field, while a small half scattering angle describes a strongly bundled light field.
A projector of the above named type generally has a high light yield. In the case of a wide light field however, the exiting light beams form a region of high light density by their convergent beam course, and so thermal UV loading in the surroundings of the projector can be large. Moreover, influencing the exiting light beams requires additional diffusion plates in front of the protective plate in order to effect a light field with an optimum light distribution for a range of half scattering angles. However, such an arrangement cannot be used to optimize the light field for a large range of half scattering angles.
Moreover, use is made of projectors having a spherical reflector, a stationary lamp at the center of curvature of the reflector, and a stepped lens arranged in front thereof. In order to set the desired light field, the arrangement consisting of reflector and lamp is moved relative to the stepped lens, and an expansion or bundling of the light field is attained in this way. Such a projector can be used to set the optimum light field over a large range of half scattering angles, and to adjust it continuously, although the projector generally has a poor efficiency and, in particular, requires heavy step lenses to shape the exiting light beams for projectors having large powers.